1. Field of the Invention
The invention relates to photo-optical keyboards. More specifically, the invention relates to an improved keyboard housing and keys for a photo-optical keyboard.
2. Description of the Prior Art
A photo-optical keyboard has a matrix of rows and columns of keys. The keyboard further has a matrix of optical paths (i.e. light channels) with a light channel for each row and each column. A light source is placed at one end of each light channel and a photo-receptor at the other end. When a key is depressed the light is blocked in the respective light channels for the row and column of the key. Decoding logic will determine which key in the matrix is depressed. The basic principles for photo-optical keyboards are shown in U.S. Pat. No. 3,056,030.
Up to this time, no commercial systems have been marketed because of the cost associated with overcoming design and manufacturing problems. Some prior art photo-optical keyboards (U.S. Pat. No. 3,856,127) have attempted to put the light channels for the columns and rows in different planes so they do not intersect. This requires that the holes either be drilled in the plastic keyboard or that the keyboard be molded in three pieces. Drilling is expensive and problems of the drill "walking" are present in attempting to drill holes at an angle for a diagonal matrix. Molding the keyboard in three pieces introduces alignment problems because of warpage and shrinkage in molded plastics.
U.S. Pat. No. 3,796,880 shows an assembly with the light channels formed by sandwiching two plates together. A portion of each of the channels is in each plate. If molded plastic pieces are used, alignment, shrinkage and warpage problems occur at the interface of the plates. This could prevent the keys from moving easily and could also cause light leakage between light channels thus producing false signals.